Puck for cathodic arc coating with continuous groove to control arc

ABSTRACT

A puck for providing a coating material in a cathodic arc coating system has a generally uniform depression formed at the outer periphery. The depression ensures that an arc from the coating apparatus will move uniformly about the outer periphery of the puck, such that a coating cloud will also be uniformly applied to parts to be coated.

RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.11/838,253, filed 14 Aug. 2007.

BACKGROUND

This application relates to an electrode puck for use in cathodic arccoating wherein a continuous groove is formed to aid in the manipulationof the movement of the electric arc, and eliminate a tendency to stallin a pore in the puck.

Cathodic arc coating systems are known, and typically include oneelectrode or cathode formed of coating material. Typically, the puck isthe cathode. Electrical connections are made to both the cathode, andtypically a chamber surrounding the cathode. The chamber is typicallyconnected to be an anode.

An electrical arc travels around the cathode which causes theevaporation of the cathode material as a vapor cloud at the spots wherethe arc touches the puck. A magnetic force is induced around thecathode, and this magnetic force aids in steering the arc around theperimeter of the puck, thus, the vapor cloud is formed around thecircumference of the surface of the cathode. Parts to be coated arelocated in the path or throw of this cloud. The magnetic force isrotated to cause the arc to move continuously around the cathode. Inthis manner, a cloud is formed uniformly about a central axis of thecathode puck, and the parts are evenly coated.

However, in practice, there is one concern wherein the puck may have aporosity that causes the arc to stall within a pore and the magneticfield which helps steer the arc cannot overcome the geometricalconstraints encountered by such porosity. That is, the arc will notcontinue to rotate uniformly about the puck and thus the vapor cloudwill not be formed uniformly within the chamber. When this occurs, thecoating deposited onto the parts is not uniform.

SUMMARY

In a disclosed embodiment of this invention, a cathode puck is formedwith a continuous depression such that the likelihood that the arc willstall in any pore is greatly reduced as it will be preferably guidedthrough the geometrically favorable depression providing more uniformmovement of the arc and subsequent formation of the vapor cloud.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cathodic arc coating system.

FIG. 2 shows a prior art puck.

FIG. 3A shows the ideal operation of the prior art puck.

FIG. 3B shows the prior art puck after the ideal operation.

FIG. 4A shows a problem in the prior art.

FIG. 4B shows the shape of the prior art puck if this problem occurs.

FIG. 5A shows the operation of an inventive puck.

FIG. 5B shows the shape of the inventive puck after the beginning ofcoating operations.

DETAILED DESCRIPTION

A cathodic arc coating system 20 is schematically illustrated in FIG. 1.A puck 22 is formed of a material to be consumed to provide a coating onparts 28 which are located within a housing 34. A so-called stinger 26communicates electrical energy to the puck 22. The stinger carriesrotating magnets as known. The parts to be coated 28 rotate along adrive axis 30, as known in the prior art. Turbine blades are but oneexample of parts coated in this manner. A trigger arm 31 is also shown.

A biased power supply 32 and a cathode power supply 24 are connected tothe chamber housing 34 and the stinger 26. As known, with operation ofprior art systems, a rotating magnetic field moves uniformly and steersthe electrical arc around the puck 22. A positively charged vapor cloud38 is formed which moves outwardly, resulting in coating of thenegatively biased parts 28. As the coating occurs, the puck 22 isconsumed.

FIG. 2 shows the prior art puck 22 having a generally cylindrical outersurface 40.

FIG. 3A shows the ideal operation of this prior art system. As shown,the outer periphery of the puck 40 has a point 52 where the electric arcis initially struck by a trigger and is subsequently steered around theouter periphery of the puck 40 by the magnetic field 56 induced by themagnets 50. As the magnets continue to rotate, the arc, and hence thecontact point 52, should move uniformly circumferentially around theouter periphery of the puck 40. Thus, as shown in FIG. 3B, with someuse, the puck 22 could have a locus of arc-struck points around theperimeter of the puck resulting in a depression 52 which is generallyuniform around this outer periphery. If the wear on the puck is uniform,then the volume of the cloud should be uniform, and the parts 28 shouldbe uniformly coated.

A problem with the prior art is illustrated in FIG. 4A. As shown in FIG.4A, there is often a porous condition at the outer periphery of the puck40. Thus, pores 152 and 54 are shown in FIG. 4A. The rotating arc maybecome trapped in any one of these pores and will not rotate smoothlyaround the puck. When this occurs, the coating vapor cloud will not beuniform, and the parts will not be uniformly coated. As shown, forexample in FIG. 4B, the pore from FIG. 4A has now grown to be quitelarge as shown at 60. This is due to the arc having been trapped in theoriginal pore.

FIG. 5A shows an inventive puck 170 having cylindrical outer surface172, and a groove 174. The groove 174 will allow the arc to avoid anypores. The problematic porosity tends to be at the outer periphery ofthe puck 170, and thus the positioning of the groove 174 at the outerperiphery will cause the arc to move uniformly, and will avoid it beingstuck in any of these surface pores 76 (see FIG. 5A). FIG. 5A shows apuck 170 wherein the groove 174 is not at the top, but spaced slightlydownwardly.

As shown in FIG. 5B, after some use, the puck 170 will have a deepergroove 174, and will resemble the groove of FIG. 3B. Once the arc hasrotated about the puck evenly for some time, the temperature of the puckincreases, generally to a red hot condition. This will help close up theremaining pores, decreasing the likelihood of the arc becoming trappedoutside of the groove.

In summary, the present invention provides a continuous depression in anouter periphery of a puck to ensure the arc will move continuously anduniformly during the initial use of the puck during the coating process.This provides a favorable path for the arc to travel around theperiphery of the puck during the beginning of the coating process, asthe circumferential groove would in most cases be deeper than theporosity encountered in the outer surface of the cathode. Whiledisclosed as the cathode, the puck can also provide the anode.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

1. An electrode puck for use in a cathodic arc coating systemcomprising: a puck body having a generally cylindrical outer surface;and a depression formed continuously about a periphery of said generallycylindrical outer surface, said depression being formed closer to oneend of the puck body than a second end, said depression being on thepuck prior to use of the puck within said cathodic arc coating system.2. A cathodic arc coating system comprising: a housing, and an electrodewithin the housing, electrical connections to both said electrode andsaid housing; part holders to receive parts to be coated located aboutan axis of said electrode; and a puck formed of a coating material, theelectrode creating an arc about the puck, said puck having a generallycontinuous depression to assist the arc to move uniformly about an outerperiphery of the puck, said depression being formed closer to one end ofthe puck body than a second end before said electrode initially createsthe arc about the puck.
 3. The system as set forth in claim 2, whereinsaid depression is already on the puck when the puck is initially placedin the housing.
 4. The system as set forth in claim 2, wherein the puckand electrode provide a cathode.